Specifications

aliased signal. Amplification and bandpass anti-alias filtering on the
453.125 kHz signal occurs on the options board.
The other signal that comes from the options board is a DC signal, also
switched in on J20, that results from noise figure measurements. This DC
signal is sampled and subsequently averaged in the DSP.
Reference Channel
Intermediate
Frequency Path
Similar to the Test Channel, the Reference Channel I.F. Chain amplifies,
samples, and filters the reference signal after it has been down converted
to a fixed intermediate frequency. Both the test and reference signals
originate at the Source module. The Source generates a 10 MHz to 3 GHz
sinusoid and this signal is routed to either the Auto-Reversing Module, or
the Non-Reversing Module, depending on the system configuration. In the
A.R.M. (or the N.R.M.), a coupler separates this single signal into two sig
-
nals, one of which becomes the reference input to the Down Conversion
Module and the other becomes an output to one of the front panel ports.
The signal sent out the front panel becomes the test signal, as it goes
through the DUT, and the signal internally routed to the Down Converter
module is the reference signal.
The I.F. chain used to process the reference signal is similar to that for
the test signal. Since the reference signal is approximately the same level
for both reversing and non-reversing system configurations, the value of
the input amplified gain is fixed at 5.2 dB. The reference signal passes
through a 5th order elliptical lowpass filter, and into a gain range ampli-
fier, U13.
Gains of 10 dB or 30 dB can be chosen with the R_GR1 bit. The process of
gain ranging on the reference channel is similar to that in the test chan-
nel, however reference channel gain ranging is only performed in the har
-
monic measurement mode. In this mode, the source harmonic is used as
the reference signal and must be amplified to achieve better resolution af
-
ter ADC conversion. In all other measurement modes, the reference chan
-
nel signal level is high enough so that gain ranging is not necessary.
In addition to switching of the options board output into the reference
channel ADC (J17), since the reference signal level is always relatively
high, switching of the analog monitor and rear panel ADC is done at the
end of the reference channel chain. If this switching were done into the
test channel, leakage of noise and high level signals through the switches
onto a low level test channel signal would be a concern.
The analog monitor multiplexes +28V, the two bias voltages, +5V, -13.4V,
+6.5V, -10V and the noise source +28V onto the ANA_MUX line after ap
-
propriate division. This line is switched into the reference channel A/D by
the EXT_SW1, SW_MON, and direct in bits. The rear panel external A/D
input allows the user to inject a signal directly into the reference channel
A/D through J25, controlled by the EXT_SW2, EXT_SW1, SW_MON and
direct in bits in a serial switch arrangement.
2-12 MS462XX MM
RECEIVER MODULE THEORY OF OPERATION